Splitting one table based on criteria and comparing - sql

Question

I'm not quite sure on the best way to phrase this particular query, so I hope the title is adequate, however, I will attempt to describe what it is I need to be able to understand how to do. Just to clarify, this is for oracle sql.
We have a table called assessments. There are different kinds of assessments within this table, however, some assessments should follow others in a logical order and within set time frames. The problems come in when a client has multiple assessments of the same type, as we have to use a fairly inefficient array formula in excel to identify which 'full' assessment corresponds with the 'initial' assessment.
I have an earlier query that was resolved on this site (Returning relevant date from multiple tables including additional table info) which I believe includes a lot of the logic for what is required (particularly in identifying a corresponding event which has occurred within a specified timeframe). However, whilst that query pulls data from 3 seperate tables (assessments, events, responsiblities), I now need to create a query that generates a similar outcome but pulling from 1 main table and a 2nd table to return worker information. I thought the most logical way would be be to create a query that looks at the assessment table with one type of assessment, and then joins to the assessment table again (possibly a temporary table?) with assessment type that would follow the initial one.
For example:
Table 1 (Assessments):
Client ID Assessment Type Start End
P1 1 Initial 01/01/2012 05/01/2012
Table 2 (Assessments temp?):
Client ID Assessment Type Start End
P1 2 Full 12/01/2012
Table 3:
ID Worker Team
1 Bob Team1
2 Lyn Team2
Result:
Client ID Initial Start Initial End Initial Worker Full Start Full End
P1 1 01/01/2012 05/01/2012 Bob 12/01/2012
So table 1 and table 2 draw from the same table, except it's bringing back different assessments. Ideally, there'd be a check to make sure that the 'full' assessment started within X days of the end of the 'initial' assessment (similar to the 'likely' check in the previous query mentioned earlier). If this can be achieved, it's probably worth mentioning that I'd also be interested in expanding this to look at multiple assessment types, as roughly in the cycle a client could be expected to have between 4 or 5 different types of assessment. Any pointers would be appreciated, I've already had a great deal of help from this community which is very valuable.
Edit:
Edited to include solution following MBs advice.
Select
*
From(
Select
I.ASM_SUBJECT_ID as PNo,
I.ASM_ID As IAID,
I.ASM_QSA_ID as IAType,
I.ASM_START_DATE as IAStart,
I.ASM_END_DATE as IAEnd,
nvl(olm_bo.get_ref_desc(I.ASM_OUTCOME,'ASM_OUTCOME'),'') as IAOutcome,
C.ASM_ID as CAID,
C.ASM_QSA_ID as CAType,
C.ASM_START_DATE as CAStart,
C.ASM_END_DATE as CAEnd,
nvl(olm_bo.get_ref_desc(C.ASM_OUTCOME,'ASM_OUTCOME'),'') as CAOutcome,
ROUND(C.ASM_START_DATE -I.ASM_START_DATE,0) as "Likely",
row_number() over(PARTITION BY I.ASM_ID
ORDER BY
abs(I.ASM_START_DATE - C.ASM_START_DATE))as "Row Number"
FROM
O_ASSESSMENTS I
left join O_ASSESSMENTS C
on I.ASM_SUBJECT_ID = C.ASM_SUBJECT_ID
and C.ASM_QSA_ID IN ('AA523','AA1326') and
ROUND(C.ASM_START_DATE - I.ASM_START_DATE,0) >= -2
AND
ROUND(C.ASM_START_DATE - I.ASM_START_DATE,0) <= 25
and C.ASM_OUTCOME <>'ABANDON'
Where I.ASM_QSA_ID IN ('AA501','AA1323')
AND I.ASM_OUTCOME <> 'ABANDON'
AND
I.ASM_END_DATE >= '01-04-2011') WHERE "Row Number" = 1

Answer 1

You can access the same table multiple times in a given query in SQL, simply by using table aliases. So one way of doing this would be:
select i.client,
i.id initial_id,
i.start initial_start,
i.end initial_end,
w.worker initial_worker,
f.id full_id,
f.start full_start,
f.end full_end
from assessments i
join workers w on i.id = w.id
left join assessments f
on i.client = f.client and
f.assessment_type = 'Full' and
f.start between i.end and i.end + X
/* replace X with appropriate number of days */
where i.assessment_type = 'Initial'
Note: column names such as end (that are reserved words in Oracle SQL) should normally be double-quoted, but from the previous question it looks as though these are simplified versions of the actual column names.

Answer 2

From your post, I assume that you're using Oracle here (as I see "Oracle" in the question).
In terms of "temp" tables, Views come right to mind. An Oracle View can give you different looks of a table which is what it sounds like you're looking for with different kinds of assessments.
Don Burleson is a good source for anything Oracle related and he gives some tips on Oracle Views at http://www.dba-oracle.com/concepts/views.htm